Since plated steel plates, particularly, galvanized steel plates have excellent corrosion resistance, they are widely used not only as typical building materials and exterior parts of home appliances requiring a finished surface, but also for exterior of vehicle parts.
Specifically, recently popular color steel plates and hot-dip galvanized steel plates for home appliance interior and exterior parts and vehicles require excellent surface qualities as well as excellent corrosion resistance.
FIG. 1 is a schematic view illustrating a process of galvanizing a steel plate in the related art. Referring to FIG. 1, a steel plate 100 continuously discharged from a cold-rolled coil by a payoff reel (not shown) and a welder (not shown) is heat-treated in a heating furnace 110 to eliminate residual stress, and then, the heated steel plate 100 is maintained at proper temperature for galvanizing, and is introduced to a plating tank 130 filled with a plating solution, that is, molten zinc 130a. 
A snout 120 connects the heating furnace 110 to the plating tank 130 to prevent the surface of the heated steel plate 100 from being oxidized by air. The snout 120 may be filled with inert gas as atmospheric gas to prevent plating defects due to surface oxidization.
After passing through the heating furnace 110, the snout 120, a sink roll 132 of the plating tank 130, and stabilizing rolls 134, a plating amount of the steel plate 100 is adjusted to a desired value by an air knife 140 disposed at the vertical upper side of the plating tank 130.
After that, the steel plate 100 passes through a skin pass mill (not shown), and surface roughness and shape are properly modified. Then, the steel plate 100 is cut by a cutter (not shown), and is rolled by a tension reel (not shown), to thereby obtain a final plated coil.
Referring to FIG. 2, evaporated zinc (curled arrows in FIG. 2) are processed to be zinc ash 130b deposited on the inner wall (inner surface) of the snout 120. When a deposited amount of the zinc ash 130b is over a predetermined threshold, the zinc ash 130b falls down and floats on the surface of the molten zinc 130a, and may be attached to the surface of the steel plate 100, thereby causing surface defects.
For example, such zinc ash may be formed by the evaporation and condensation of zinc, stagnation of atmospheric gas within a snout, and waves due to the movement of a steel plate into the surface of a plating solution, and is typically a Zn or ZnO compound.
Since zinc ash is a pollutant source for a steel plate, that is, a source of pollutants causing line defects and plating defects on the surface of a steel plate, zinc ash may be a serious defect in a high-grade galvanized product.
Various methods are introduced to reduce or prevent the production of zinc ash within a snout. For example, evaporation of zinc may be fundamentally prevented, the surface of molten zinc within a snout may be decreased, certain types of gas may be injected into a snout, or zinc ash or zinc vapor may be collected.
However, these methods have limitations in suppressing the evaporation of zinc to effectively prevent zinc ash from being deposited and grown on the inner wall of a snout.
Particularly, when zinc ash or zinc vapor is collected and removed, an atmospheric condition required within a snout may be jeopardized. In addition, a through collecting process is required to efficiently collect and remove zinc vapor or zinc ash from within a snout, and thus, operating costs may be increased. Moreover, in this case, zinc ash removing efficiency may be degraded.
Furthermore, a dross oxide may be formed by contact between atmospheric gas or air (oxygen) and the surface of molten zinc within a snout. A dross oxide may be difficult to efficiently remove using a typical method of collecting and removing zinc ash within a snout.
Moreover, a technology of using an induction current generated by time travelling magnetic flux that varies magnetic field, to apply drag force and levitation force to zinc ash or dross formed of zinc or zinc oxide as a diamagnetic substance, thereby forcibly guiding the zinc ash or dross to a suction line has not been disclosed.